Recoil device for a rotary forging mill

ABSTRACT

Operating a rotary forging mill with a gas recoil device by compressing the recoil gas to a limit pressure and then keeping the recoil gas at approximately the same pressure as the recoil piston continues its rearward travel.

I Umted States Patent [151 3,638,466

Calmes 1 Feb. 1, 1972 [54] RECOIL DEVICE FOR A ROTARY [56] References Cited FORGING MILL alm UNITED STATES PATENTS 721 t: -PIC EP ,LMt- 1 fj g g j e on 2,088,134 7/1937 Haessler ..92/134 x 2,775,150 12/1956 McLay ..72/208 22] Filed: June 19, 1969 Prima Examiner-Andrew R. .luhasz 21 A l.N.. 4832 l 1 pp 0 83 Assistant Examiner-James F. Coan Attorney-Brown, Murray, Flick 8: Peckham [30] Foreign Application Priority Data June 20, 1968 Germany ..P 17 52 603.3 [57] ABSTRACT Operating a rotary forging mill with a gas recoil device by U.S. l 9, compressing the recoil gas to a pressure and then keeping [51 Clthe recoil gas at approximately the same pressure as the recoil Fleld of Search 4 l piston continues its rearward travel 6 Claims, 6 Drawing Figures RECOIL DEVICE'FOR'A ROTARY-FORGING MILL This invention relates to a method of operating a recoil device for fonning seamless tubes. on a rotary forging mill (also called a pilger mill), which device essentially has a recoil cylinder, a recoil piston with a mandrel and a device for braking'the forward movement of the, piston; a cylinder space behindthe piston contains gas, for-instance air,.for storing the energy for the forward stroke of the piston. The braking device may be in the form ofa cone containing liquid, and the recoil device may include a mechanism for turning themandrel. This invention also relates to a device for carrying out the method.

When using a rotary forging mill to roll a hollow into atube, the recoil piston is moved back by the working part-of the rolls-During this working stroke, the gas contained in the rear cylinder space of the recoil cylinder is compressed.'At the end of the working stroke, when the. hollow has been released from the .workingpart of the rolls, the. compressed; gas. drives'the recoilpiston forward so that'the hollow-and'the mandrel are again passed between therotary forgingrolls for a further rolling cycle-During this forward movement, the recoil piston together with the mandrel and the hollow may be turned throughsay 90by means of aturning mechanism-so. that the ridges or flashes caused by the spaces between the edges of the rolls are rolled out during the course of the next rolling cycle. The recoil piston can be braked for example by arranging for the recoil piston to enter the braking cone or funnel of a liquid brake towards the end of the, forward stroke.

A limit is set on the compression of the recoil,- gas inthe rear cylinder space of the recoil cylinder, in particular forthe following reasonsythe rotary forging rolls-havea workingpart which-is made up of threesections. The'first section, the socalledcaliber mouth,tgrips the hollow. This piece of the rolls is also called the caliber trumpet section and performs the deformation work. The smooth sectionof the working part is adjacent the caliber mouth, and smoothes the already rolled-out tube. In both these sections, the tube.is-tightly-surrounded by the caliber. -In the zone of 'the third section, the tube is gradually released'from the rolls. .Uptothepresent day, the

-tubes,:transv,erse cracks can occur in'the tube wall if the'thin tube wall-can .no longer transmit the recoilzforce as a resultof the-counterpressure of the recoil air-'being too great.

According to azfirst aspect ofthepresent invention, thereis provided amethod of operating a rotary forging-mill for'forrning seamless tubes, the rotary forging mill having a recoil device .with a recoil cylinder, a recoil piston in the recoil cylinder, :the recoil cylinder defining a space behind the recoil piston, a mandrel connected to the recoil piston, and braking means for braking the forward movement of the piston, in which method, during the-working (rearward) stroke of the recoil piston, the gas pressure-in said space is compressed to a 7 *limit pressure and the gas pressure in said space is subw sequently kept approximately. constant.

According to a second aspect of this invention, there is provided a recoil device for a rotary forging mill, the recoil device having a recoil cylinder,

a recoil piston in the recoil cylinder, the recoil cylinder defining a space behind the recoilpiston, the recoil piston being arranged to have a mandrelconnected thereto,

displaceable means closing said space, the displaceable means .being arranged to be displaced when the pressure in said space reached a limit pressure,

agas container of substantiallylargerrcubic capacity than the volume of the recoilcylinderswept by the recoil piston, connectedto a space behind 'the displaceable means, and

brakingmeansfor brakingthe forward movement of 'the 'recoil piston. Using this invention, the potential-energy in the recoil air in the rear space of the recoilzcylinderis so increased that the force on therecoilpiston is notincreased substantially above acertainlimiting value and atthe same time the-travel caused-by the inertia-oftthe withdrawn masses (recoil piston,'mandrel and hollow.) can be decreased while achieving agreatforward speed during thereturn stroke of the piston.

Although it is theoretically feasible to use other means such as a very large relief valve, the displaceable means is preferably a movable closure piston movable-in a cylinder (which cylinder is most convenientlythe recoil cylinder), the front of themov-able closurepistonbeingin communication with said space and the rear of the movableclosure piston being in communicationwith'the gas-container; in this manner themovable closure piston closes saidspace and, after said limit-pressure is'reached in saidspace, the.gas;pressurein said space is subsequently kept approximately constant by rearward movement of the movable closure; piston. ltis'not-essential to alter the end position of the movable closure pistonwith every change in the rolling program, though some alteration may be required with some changes.

Particularly during the starting or.pointing period, thelrearward movement of the recoil pistonmayzbe assisted by subjecting the forwardside of :the=recoil;.piston -.to increased .gas pressure, preferablybyintroducing:acompressed gas into the forward space in therecoil eylinder.: For.this purpose,inlet and outlet valve means may be :provided for passing compressed gas into or releasing compressedgas from the-space defined bythe recoil cylinder in front .of'the recoil'piston. "By the compression offthc recoil air which is achieved in this manner, the starting or pointingperiodcan-be carried out with large forwardspeedsofathe recoil :piston, and hence at high speeds of'rotation ofthe rotaryforgingsrolls.

Said ilimit .pressure 1 in "the space behind &the :recoil .piston is preferably adjustable, and means may be :provided for con- :trolling the initialpressure .inthe gascontainer to azpredetermined, adjustable value.

This invention'extends to a rotary:forging mill including the recoil device of thesecondaspect of theinvention.

The invention will be'further'described,'by way of example, with reference to the accompanying schematic drawings, in which:

FIG. 1 is a longitudinal section through :an earlier recoil device for a rotary forging mill;

FIG. 2 is a longitudinal section corresponding to FIG. 1, showing therecoil deviceinanother position during its working stroke;

FIG. 3-is a graph of the compression'curve during the working stroke of the recoil deviceofFIGS. *1 and 2;

FIG. 4 is a longitudinal section through-arecoil device in accordance with the invention, shown at the "beginning of its working stroke;

FIG. 5 is a longitudinal section through the recoil device of FIG. 4, shown at the end of its working stro'ke;and

FIG. 6 is a graph ofthe compression curve during the working stroke of the recoil device ofFIGS. 4 and 5.

The earlier recoil device of FIGS. -1 and 2 has arecoil piston 1 and a recoil cylinder 2. The :rear space 3 of the recoil cylinder 2 is closed by an end closure'4 which is carried by a threaded spindle 5. According to the diameter of the tube to be rolled, the cubic capacity of the rear space 3 canbe altered by adjusting the end closure 4 whose threaded spindle 5 can turn in a nut 6 carried by a cylinder end cover 7.

FIG. 3 is a graph of the compression curve for the recoil air in the rear space 3. The initial pressure of the air in the rear space 3 is indicated as P,,.

This pressure P occurs in the position of the recoil piston shown in FIG. 1. During the movement of the recoil piston 1 in the working stroke, the recoil air in the rear cylinder space 3 is compressed up to a pressure I along the compression curve A, B, C. The line D indicates the position of the end closure 4 and the line E indicates the position of the fluid brake of the recoil device.

Using the recoil device of FIGS. 1 and 2, it is indeed possible to roll a large range of tube diameters with the same recoil device by adjusting the-cubic capacity of the space 3 to the required length of working stroke. However, as the roll diame' ter becomes smaller as a result of the pilger rolls being turned, and with every alteration of the rolling program, the end closure 4 must be adjusted. This adjustment takes some time before the correct position is found. Furthermore, the recoil device and the tube can be considerably damaged if the readjustment of the end closure 4 is forgotten when changing from a small to a large working stroke.

FIGS. 4 and 5 show a recoil device constructed according to the invention. The recoil piston 8 moves in a recoil cylinder 9. A movable piston closure 11 is mounted in the rear space of the recoil cylinder 9. By this arrangement, a further space 12 is provided, connected by means of a duct with an air container 13 whose cubic capacity is considerably larger than the maximum capacity of the space 12. The pressure in the air container 13, and thus the pressure in the space 12, can be adjusted to the value required at any time, for instance by means of a compressor.

The forward space 17 of the recoil cylinder 9 is in communication with an inlet valve 18 and an outlet valve (not shown). A compressed gas is passed through the inlet valve 18 to the front of the recoil piston 8 in order to assist the rearward movement of the recoil piston 8, particularly during the pointing or starting period. The outlet valve serves to exhaust the compressed gas during the ensuing forward stroke. FIG. 5 shows the rearmost position of the recoil piston 8. After reaching an adjustable limit pressure in the rear space as a result of the compression of the recoil air in the rear space 10, the movable piston closure 11 moves rearwards out of the position shown in FIG. 4 with the same speed as the recoil piston 8. It is possible to equalize the pressure on the forward and rear sides of the movable piston closure 11 because of the cubic capacity of the air container 13 is considerably larger than the space 12. In this way, the compressed air can have a large potential energy which is available for great acceleration of the whole mandrel during the subsequent forward stroke.

FIG. 6 shows a graph of the compression curve which can be obtained with the recoil device of FIGS. 4 and 5, the position of the fluid brake and the end position of the movable piston closure 11 being the same as the position of the fluid brake and of the fixed end closure 4 shown in FIG. 3, thus giving a comparison between the two compression curves. In FIG. 6, the line F indicates the position of the fluid brake and the line G indicates the end position of the movable piston closure 11. In addition, line H in FIG. qjggipgtgstheinjtial posi- M...-. tion of-themovablepisit'fi' arasar'n. The initial pressure of the recoil air in the rear space 10 of the recoil cylinder 9 is indicated as P During the working stroke, the compression curve AB rises more steeply than the compression curve shown in FIG. 3 and after a considerably shorter movement of the recoil piston 8, reaches a permitted limiting pressure P, because the rear space 10 is made smaller by the position of the movable piston closure 11 shown in FIG. 4. On reaching the adjustable limiting pressure P,, which is determined by the pressure in the air container 13 and the pressure in the space 12, the piston closure 11 moves rearwards at the same speed as the recoil piston 8 because, as a result of the large air container l3, practically no further compression occurs i'n'the space 12.. This part of the working stroke is shown by the curve BC, which here indicates a slight increases in pressure in the rear cylinder space 10 of the recoil cylinder 9 because the air container 13 is not infinitely large.

The forward position of the movable piston closure 11 is in general the same for all rolling programs. If it is however necessary to make the compression curve AB somewhat steeper or somewhat flatter, the forward position of the movable piston closure 11 can be altered. For this purpose, the movable piston closure 11 has a stroke-limiting rod 14 which passes through a central bore in a recoil cylinder closure cover 15 and outside carries an adjustable nut 16; by turning the nut 16, the forward position of the movable piston closure 1 I can be adjusted.

The advantage of the construction shown is that high rolling speeds of rotation can be achieved without the pressure of the recoil air at the end of the working stroke becoming so great that there is a danger of the tube slipping in the third caliber part (the end of the working part) of the pilger roll or of the tube tearing when rolling out thin-walled tubes. The speed of rotation of rolls having a caliber of 250 mm. diameter can for instance be increased from about 68 to about I 12 rpm, that is to say by about 65 percent. In this manner, the rolling efiiciency is not only increased, but the rolled tubes have a considerably better quality and a higher temperature on leaving the mill and a greater length. This furthermore has a beneficial effect on tooling costs and on steel yield.

In addition, a comparison of the two compression curves of FIGS. 3 and 4 shows that during the forward stroke, when the compression curves run in the opposite direction, a considerably smaller amount of braking work is required with the device of FIGS. 4 and 5 than with the device of FIGS. 1 and 2.

I claim:

1. A method of operating a rotary forging mill for forming seamless tubes, the rotary forging mill having a recoil device with a recoil cylinder, a recoil piston in the recoil cylinder, the recoil cylinder defining a space behind the recoil piston, a closure piston in said space, a mandrel connected to the recoil piston, and braking means for braking the forward movement of the piston, the method comprising compressing the gas in said space between said pistons to a limit pressure by means of the recoil piston during part of its rearward working stroke, and then moving the closure piston rearwardly by means of said compressed gas at approximately the same speed as the recoil piston during the remainder of said working stroke to maintain the gas pressure in said space approximately constant.

2. A method as claimed in claim 1, wherein the rearward movement of the recoil piston is assisted by subjecting the forward side of the recoil piston to increased gas pressure.

3. A recoil device for a rotary forging mill, the recoil device having a recoil cylinder, a recoil position in the recoil cylinder, the recoil cylinder defining a space behind the recoil piston, the recoil piston being arranged to have a mandrel connected thereto, displaceable means closing said space, the displaceable means being arranged to be displaced when the pressure in said space reaches a limit pressure, a gas containe r ofsubttli na tiallyNIargerWcubic capacitythan"the waists of the recoil cylinder swept by the recoil piston, connected to a space behind the displaceable means, and braking means for braking the forward movement of the recoil piston.

4. A recoil device as claimed in claim 3, wherein the displaceable means is a movable closure piston movable in a cylinder, the front of the movable closure piston being in communication with said space and the rear of the movable closure piston being in communication with the gas container.

5. A recoil device as claimed in claim 3, wherein means are provided for controlling the initial pressure in the gas container to a predetermined, adjustable value.

6. A recoil deyiceclaimed in claim into ro releasing compressed gas from the space defined by the recoil cylinder in front of the recoil piston.

V j 3, wherein inletand I outlet valve -means are provided for passing compressed gas UNITE-D- STATES PATENT 'OFFECE v CERTIFICATE. OF CURRECTION Patent No. 31 3 1 4 Dated February 97 Inventor'(s) Jean- Paul Calmes It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

lai-m 3,' 111152, change "position" to --piston--.

I Signed and eealed this 30th day of May 1972.

(SEAL) Abtest:

ROBERT GOTTSCHALK EDWARD P-LFLE-TCHERJR,

Commissioner of Patents Attesting Officer FORM PO-iOSO (10-69) USCOMm- 50375 259 u.s, GOVERNMENT PRINTING ornc: I959 o-aee-au 

1. A method of operating a rotary forging mill for forming seamless tubes, the rotary forging mill having a recoil device with a recoil cylinder, a recoil piston in the recoil cylinder, the recoil cylinder defining a space behind the recoil piston, a closure piston in said space, a mandrel connected to the recoil piston, and braking means for braking the forward movement of the piston, the method comprising compressing the gas in said space between said pistons to a limit pressure by means of the recoil piston during part of its rearward working stroke, and then moving the closure piston rearwardly by means of said compressed gas at approximately the same speed as the recoil piston during the remainder of said working stroke to maintain the gas pressure in said space approximately constant.
 2. A method as claimed in claim 1, wherein the rearward movement of the recoil piston is assisted by subjecting the forward side of the recoil piston to increased gas pressure.
 3. A recoil device for a rotary forging mill, the recoil device having a recoil cylinder, a recoil position in the recoil cylinder, the recoil cylinder defining a space behind the recoil piston, the recoil piston being arranged to have a mandrel connected thereto, displaceable means closing said space, the displaceable means being arranged to be displaced when the pressure in said space reaches a limit pressure, a gas container of substantially larger cubic capacity than the volume of the recoil cylinder swept by the recoil piston, connected to a space behind the displaceable means, and braking means for braking the forward movement of the recoil piston.
 4. A recoil device as claimed in claim 3, wherein the displaceable means is a movable closure piston movable in a cylinder, the front of the movable closure piston being in communication with said space and the rear of the movable closure piston being in communication with the gas container.
 5. A recoil device as claimed in claim 3, wherein means are provided for controlling the initial pressure in the gas container to a predetermined, adjustable value.
 6. A recoil device as claimed in claim 3, wherein inlet and outlet valve means are provided for passing compressed gas into ro releasing compressed gas from the space defined by the recoil cylinder in front of the recoil piston. 